Recently, as industrial technologies have developed, ceramic materials without conduction electrons and having insulation for insulating electricity and heat and stability in strong coupling to have a high melting point and chemical stability are used as electronic materials in various ways.
Particularly, ceramic materials are generally used as piezoelectric materials that output electricity when receiving pressure or deform when receiving electricity.
A piezoelectric ceramic technology described above indicates a technology of forming a module that generates electricity when a physical pressure is applied thereto, with a ceramic element. Here, a piezoelectric element indicates an element having properties capable of mutually converting electrical energy and mechanical energy.
Here, in the piezoelectric element, a voltage is generated by a force applied to piezoelectric ceramic and a level of the generated voltage changes according to the intensity of the force.
Also, it is known that a piezoelectric ceramic element described above has properties of precisely controlling a displacement with high responsibility and a stacked piezoelectric ceramic element is able to obtain a high displacement using a small voltage.
Due to a reason as described above, stacked piezoelectric ceramic elements are generally applied to and used for an injector, a micro pump, an inkjet head, and a speaker.
General stacked piezoelectric ceramic elements have a structure in which an actuator stacking body having a structure in which a piezoelectric actuator ceramic layer and an internal electrode are alternately stacked is formed and an external electrode is formed on an uppermost layer, a lowermost layer, or a side of the stacking body.
Meanwhile, in the case of stacked piezoelectric ceramic elements, various technologies are applied to prevent insulation deterioration or insulation breakdown in a high temperature and high humidity environment.
Particularly, when micro cracks occur at the internal electrode for polarization that forms the actuator stacking body, humidity penetrates the same and insulation deterioration or insulation breakdown occurs.
To solve problems described above, hitherto, there was a technology for suppressing water penetration by forming a moisture-proofing layer therein or surrounding the internal electrode for polarization and a piezoelectric ceramic layer with inorganic materials.
However, a general technology of forming a moisture-proofing film inside a stacked piezoelectric ceramic element has a difficulty in being applied to products including an internal electrode for polarization with a large area, and a technology of suppressing water permeation by protecting an internal electrode for polarization and a piezoelectric ceramic layer has a problem in which a driving force of an actuator is deteriorated because an adequate thickness of inorganic materials is necessary.
Accordingly, a practical and applicable technology with respect to a piezoelectric ceramic element capable of preventing deterioration of insulation resistance and deterioration of a driving force in a high humidity environment is acutely required.